Prestressing method



June 27, 1967 J. w. HOWLETT 3,327,380

PRESTRESSING METHOD Filed June 8, 1964 3 Sheets-Sheet 1 INVENTOR.

2 James W How/err A 2 Attorney J1me 1967 J. wv HOWLETT 3,327,380

PRESTRESSING METHOD Filed June 8, 1964 6 Sheets-Sheet 2 INVENTOR.

Jam W Hwlen t a I June 27, 1967 J. w. HOWLETT 3,327,380

PRESTRESSING METHOD Filed June 8, 1964 5 Sheets-Sheet Z5 [07 W14 7 74 H3mm I09\ 4: lunmml 11mm es W How/eh United States Patent M 3,3273%PRESIRESSING METHGD .lames W. Hewlett, Richmond Annex, Qalii, assignorto Hewlett Machine Works, a corporation of California Filed .lnne 8,1964, Ser. No. 373,464 7 Claims. (Cl. 29-452) This invention relatesgenerally to the method of prestressing structural materials such asconcrete, steel beams and the like, and more particularly is directed tothe method of using elongated tendons that are placed in a tensionedcondition for applying prestressing forces.

The use of tensioned tendon members is well known in the prestressingart, it being the general practice to secure the tendons at oppositeends to a given structural material and applying compressiveprestressing forces to the material by placing the tendons undertension. Prestressing tendons may be broadly classified into the twocategories of wires and 'bars. Wire tendons are elongated steel membersusually having a diameter of no larger than about Mr inch, and areavailable in continuous lengths in roll form. Wires are relatively easyto handle, may be made of higher tensile strength than bars, and can bearranged in large pluralities of coextensive tendons to provide anextremely large combined tensile strength. In comparison, bar tendonsmay be several inches in diameter, and have inherent limitations intheir utility. Because bars are relatively inflexible, they are normallylimited to lengths of about 80 feet, so that they can be transported byconventional trucks or trains. Also, the

large bulk and weight of bar tendons makes them often difficult tomanipulate into their required positions.

In view of the foregoing, it is often preferable that pluralities ofcoextensive wire tendons be used where tensioning forces are to beapplied over a relatively long distance, and where relatively highforces are required. Nevertheless, however, it may still be desirable insome situations that a single large diameter bar be secured to thematerial to be prestressed, rather than having to secure a large numberof smaller wires. Accordingly, it is advantageous to couple a largeplurality of coextensive wires to single larger diameter bars, so thatthe wires extend over substantially the full length of the structuralmaterial and the bars are disposed only at the ends for securance to thematerial.

Heretofore, wire tendons have been coupled and/or secured by means of'buttonhead protuberances provided integrally at the ends of eachtendon, the protuberances being formed by a conventional metaldeformation process. The wires are extended through holes in variousanchor members, with the bottonheads subsequently being formed to bearagainst the anchor members. Where large pluralities of coextensive wiresare required, it has been the practice to assemble these wires in theshop with anchor members at each end of the wires, so that the wholeassembly becomes a substantially unitary structure which must then betransported to the construction job site.

Heretofore, there has been limited versatility in the use of wiretendons with regard to the ease of fabrication and assembly in on thethe job situations. Also, no ready means have been provided for couplingwire tendons together in end to end relation, or for coupling largepluralities of wires together in such a manner that further tendonextensions can readily be added. In addition to this previous limitedversatility in coupling and securing wire tendons, there also has notbeen provided ready means for tensioning and securing the tendons attheir ends, and further enabling ready coupling of additional tendons tothose already mounted and tensioned.

A further limitation of preassembled pluralities of wire tendons is thatthe anchor member secured to 3,327,380 Patented June 27, 1967 their endsis usually of a relatively large diameter. Consequently, such assemblyis limited with respect to the structures through which it must bestrung by the diameter of the anchor member, and difficulties arepresented where tendons must be passed through relatively small diameteropenings in structural materials.

A need has arisen in view of the above for a more versatile wire tendonprestressing apparatus, with which it is not necessary to preassemblepluralities of wires but rather which readily enable individual wires tobe strung as desired and then be easily secured to suitable anchoringstructures on the job. Likewise, a need has existed for a wireprestressing apparatus which in general has a broader field of utilitythan has been heretofore afforded, and with particular regard to theability to couple and secure wire tendons, both in pluralities ofcoextensive wires and as individual wires. r

Accordingly, an object of the present invention is to provide aprestressing method for utilizing wire tendons with great versatility invarious tensioning arrangements, wherein such wire tendons are readilycoupled or anchored to other members forming a part of the completeprestressed structure.

Another object of the invention is to facilitate the use of pluralitiesof cocxtensively disposed tensioned wire tendons, with particular regardto coupling and securing such pluralities to other tendons or members.

A further object is to provide a prestressing method for applyingtensioning force to wire tendons in a ready and quick manner, and forreadily securing the ends of wire tendons so tensioned to maintain themin the required tensioned condition.

Still another object is to provide novel and improved method forsecuring the end of a wire tendon which does not utilize theconventional integrally formed buttonhead protuberance, but rather whichemploys separate members that are readily attached to a wire tendon.

The invention possesses other objects and features of advantage, some ofwhich of the foregoing will be set forth in the following description ofthe preferred form of the invention which is illustrated in the drawingsac companying and forming part of this specification. It is to beunderstood, however, that variations in the showing made by the saiddrawings and description may be adopted within the scope of theinvention as set forth in the claims. 1

Referring to said drawings:

FIGURE 1 is a fragmentary plan view, partly in cross section, of a wiretendon and coupling means used in conjunction with the presentinvention. 1 FIGURE 2 is a fragmentary cross sectional view of two wiretendons coupled together in accordance with the present invention.

FIGURE 3 is a fragmentary cross sectional view of the instantprestressing apparatus shown with a bearing plate for transmittingtensioning forces to a concrete structure. I

FIGURE 4 is a fragmentary cross sectional View with portions broken awayillustrating a plurality of wire tendons coupled to a single largerdiameter tendon.

FIGURE 5 is a cross sectional view along the line 5-5 as shown in FIGURE4.

FIGURE 6 is a cross sectional view showing a plurality of tensioned wiretendons connected to a bearing plate for applying prestressing force toa concrete structure.

FIGURE 7 is a cross sectional view depicting jacking means applying atensioning force to a wire tendon for application to a bearing plate andconcrete structure.

FIGURE 8 is a fragmentary cross sectional View depicting prestressingapparatus used in securing two concrete beams to a concrete column.

FIGURE 9 is a fragmentary cross sectional view illustrating a pluralityof spliced wire tendons forming part of prestressing apparatus used insecuring two concrete beams to a concrete column.

FIGURE 10 is a fragmentary cross sectional view showing a modified formof wire tendon and coupling means from that shown in FIGURE 1.

FIGURE 11 is an end view of the tendon shown in FIGURE 10.

FIGURE 12 is a fragmentary cross sectional view showing another modifiedform of wire tendon and coupling means.

FIGURE 13 is a fragmentary cross sectional view of a plurality ofcoextensive wire tendons and a single larger diameter tendon all coupledto another single tendon.

FIGURE 14 is a cross sectional view along the line 14-14 shown in FIGURE13.

=Prestressing apparatus embodying the present invention generallycomprises at least one bearing plate 11 for transmitting force to astructural material to be prestressed, such as the concrete structure 12shown in FIG- URE 3, and tensionable tendon means secured to the bearingplate for applying tensio-ning force thereto. The tendon means includesa first elongated tendon, such as the wire tendon 13 shown in FIGURE 2;means defining a protuberance secured adjacent the end 14 of the tendon1 3, such as the integrally formed buttonhead 16; an externally threadedtubular sleeve member 17 disposed concentrically on the tendon 13adjacent the proturberance for abutting engagement therewith; a couplingmember having an internally threaded bore threadedly engaging the sleevemember 17, such as the internally threaded tubular member 18; and asecond elongated tendon 19 secured to the coupling member and disposedin general end to end relation with the tendon.

A basic element of the instant prestressing apparatus is a wire tendon21 as shown in FIGURE 1, having protuberances such as the integralbuttonheads 22 and 23 formed at either end of the tendon. An externallythreaded sleeve member 24 can be mounted on the tendon prior toformation of the buttonhead, whereby the sleeve 24 is adapted to engagethe buttonhead 22 in abutting relation. In some instances it may bedesirable to mount the sleeve members after the buttonhead has beenformed, and for this purpose a split sleeve 26 is provided whichincludes half-tubular segments 27 and 28 as shown in FIGURE 1. The splitsleeve 26 is of particular utility in on the job situations Where it isnecessary to couple or secure an existing buttonhead tendon that doesnot already have a sleeve 24. The segments 27 and 28, when placedtogether on a tendon, form the equivalent of a sleeve 24.

In order to coupled together two tendons disposed in generally alignedend to end relation, the internally threaded tubular coupler shown inFIGURE 2 can be used in conjunction with a pair of tendons each havingbuttonhead protubenances on their confronting ends. Thus, the wiretendon 19 is provided with a buttonhead 29 and a sleeve member 31, sothat the coupler 18 threadedly engages both sleeves 17 and 31 therebyconnecting the wires 13 and 19.

Means for securing a single wire tendon in a desired tensioned conditionis disclosed in FIGURE 3, and in this regard it is noted that thebearing plate 11 is provided with a hole 32 through which passes the endportion of a wire tendon 33. An elongated externally threaded sleevemember 34 is concentrically mounted on the tendon 33, and abuttinglyengages a buttonhead 36 on the end of the tendon. The sleeve 34 passesthrough the 'hole 32, and an internally threaded member such as a nut 37is mounted on the sleeve for axial adjustment thereon. Tensioning meansto be described pull the sleeve 34 outwardly to place the tendon 33under tension, and the nut 37 is then screwed down into abuttingengagement with the bearing plate to maintain the tendon in itstensioned condition. It is noted that the other end of the tendon 33 issuitably anchored to the concrete structure 12, so that when the tendonis tensioned a compressive prestressing force is applied to theconcrete. In the event that another tendon 38 is required to be coupledto the tendon 33, a tubular coupler 39 can be used in the same manner asdescribed with regard to FIGURE 2.

In some instances as noted hereinabove it is advantageous to use aplurality of coextensive wire tendons to achieve extremely high tensileforces, as compared to a single bar tendon of relatively large diameter.As noted, wire tendons can be provided more readily in longer lengthsthan large diameter bars or rods, and are more readily handled. Insituations to be described, it is sometimes desirable to couple a largeplurality of coextensive wire tendons to a single larger diameter bartendon, and in this regard reference is made to FIGURE 4 whereincoupling means in accordance with the present invention is provided forjoining four wires 41 to a single bar tendon 42. In more detail, each ofthe wires 41 has a buttonhead 43 and a sleeve 44 similar to thatdescribed in FIGURE 1. A coupler member 46 is provided with acorresponding number of internally threaded bores 47 which threadedlyengage the sleeves 44, thus securing the tendons 41 to the coupler 46.The bar 42 can be secured to the opposite face of the coupler 46 by anysuitable means, which as shown may comprise wedge grip coupling means ofthe type disclosed in Patent No. 2,930,642. The bar 42, of course, maybe provided with conventional threads, which would engage acomplementarily threaded bore in the coupler 46.

In FIGURE 6, there is shown a prestressing apparatus somewhat similar toa conventionalsystem. A plurality of wire tendons 48, having buttonheads49, pass through holes 51 in a bearing plate 52 which engages a concretemember 53. The wires 48 also pass through holes 54 in an anchor member56, with the buttonheads 49' being disposed on the outer side of theanchor member. As in the conventional system, the anchor member 48 canbe grasped by suitable jacking means, whereby the wires are placed undertension, and then shim members such as the two metal plates 57 areinterposed between the anchor 56 and bearing plate 52. In addition tothe structure as described thus far, which is conventional, the instantapparatus provides a plurality of externally threaded sleeve members 58on each of the wires 48 for engagement with their respective buttonheads49. Consequently, it is possible with the instant apparatus to readilycouple additional wire tendons in end to end relation with the,

Wires 48, in the manner already described with regard to FIGURES 2 and3.

A jack 61 is disclosed in FIGURE 7 for use in applying tension toindividual wire tendons having buttonheads. As shown, the jack 61includes a supporting member 62 having a pair of spider leg members 63which extend into abutting engagement with a bearing plate 64. Aconventional hydraulic means 66 is mounted on the member 62, and has apiston 67 extending axially between the legs 63 and adapted forselective reciprocating movement. A wire tendon 68 extends through thebearing plate, and has a sleeve member 69 engaging a buttonhead 71. Atubular coupler 72 has internal threads which engage the sleeve 69, andexternal threads on which is mounted an internally threaded stop membersuch as the nut 73. The piston 67 of the jack 61 is externally threadedfor engagement with the coupler 72, whereby the jack can be operated topull the wire 68 into a tensioned condition. A tubular shim member 74 isinterposed between the nut 73 and the bearing plate, and when the wireis tensioned to the desired amount the nut 73 is tightened against theshim 74 to maintain the wire in its tensioned condition. It will beappreciated that the jack 61 may also be used to apply tension to thewire 33 as shown in FIGURE 3, the piston 67 engaging the coupler 39 inthe same manner, as described with regard to FIGURE 7.

One use of wire tendons in accordance with the present invention isdisclosed in FIGURE 8, wherein a pair of concrete beams 76 and 77 aresecured to a concrete column 78. In this structure, a plurality of wiretendons 79 are coupled to a single bar 81 by means of a coupler 82 ofthe type described hereinabove with reference to FIGURES 4 and 5. Thebeam 76 is first secured to the column 79 by extending the bar 81through a bore 83 in the column, and then anchoring the bar by means ofa temporary anchor nut 84. The nut 84 may be a wedge grip nut of thetype disclosed in my copending patent application for ConcretePrestressing Apparatus, Ser. No. 302,628, filed Aug. 16, 1963. After thebeam 76 and column 78 are secured as shown, the second beam 77 can beconnected by means of another coupler 86 which joins the bar 81 toanother plurality of wire tendons 87.

In FIGURE 9, a pair of concrete beams 88 and 89 are secured to a column91, by means of a plurality of spliced wire tendons 92 which are joinedtogether by means of couplers 93 in the manner described hereinabovewith reference to FIGURES 2 and 3. The individual wires can be strungthrough openings in the beams and columns as shown, which openings neednot be any larger than necessary to accommodate only the wires. It isnot necessary to pass any anchor members through these holes, since thewires can be secured to bearing plates (not shown) in the mannerdescribed above with reference to FIGURE 3. That is, the Wires cansimply be passed through the holes in the bearing plates, after whichthe stop nuts 37 are mounted on corresponding sleeve members.

An alternative embodiment regarding the buttonhead protuberances for thewire tendons is disclosed in FIG- URES l0 and 11. In particular, insteadof the integrally formed buttonhead as described hereinabove withreference to FIGURE 1, there is shown in FIGURES and 11 a separate innertubular member 94 mounted concentrically on a wire tendon 96, and whichhas a tapered outer surface 97. The member 94 is adapted to applyradially inward force on the wire 96, and in this regard is providedwith a longitudinal slit 98. The inner bore surface 99 of the member 94is preferably provided with a serrated finish so that it will grip thewire and restrain relative axial movement between the wire and member94. An externally threaded sleeve member 101 is mounted concentricallyon the wire, and has a tapered inner surface 102 which complimentarilyengages the tapered surface 97 of the member 94. Thus, as the sleeve 101is urged toward the end of the wire 96, the tapered surfaces create aradially inward force on the inner member 94, which therefore securelygrips the wire. In the embodiment just described the inner diameter ofthe member 94 is dimensioned to form a slight interference fit with thewire 96, so that there will be an initial grip between the wire andmember 94. Another alternative embodiment is disclosed in FIGURE 12,similar to that of FIGURES l0 and 11, but wherein the inner member 94ais not dimensioned for an interference fit with the Wire 96. Rather, theend of the wire is peened over by a hammer or the like to provide aslight protuberance 103, which serves to create the initial grip betweenthe member 94a and the wire.

Where large pluralities of coextensive wires are used to provide tensileforces, it has been found that prior to application of tension to thewires they,tend to sag or drape irregularly between the points at whichthey are supported. A somewhat better natural drape is obtained with abar. A modified coupler 104 is disclosed in FIG- URES 13 and 14,somewhat similar to the coupler 46 shown in FIGURE 4, but which combinesthe greater tensile strength of wire tendons with the improved naturaldrape of a bar. More particularly, a plurality of internally threadedbores 106 are disposed in circumferentially spaced relation on one endface of the coupler 104, these bores threadedly engaging sleeves on wiretendons 107 in the same manner as described with regard to FIGURE 4. Alarge internally threaded bore. 108 is disposed concentrically withinthe smaller bores 106-, and engages the threaded end 109 of a bar 111which is of substantially larger diameter than the wires 107. Aninternally threaded bore 112 is provided on the opposite end of thecoupler 104, and engages the threaded end of another bar 113. Thecombined tensile strength of the wires 107 and bar 111 is substantiallyequal to that of the larger diameter bar 113. The advantage of thecoupled tendon structure as just described is that the center bar 111controls the desired sag while utilizing the plurality of wires toachieve the necessary tensile strength. It should be noted that the bars111 and 113 can be secured to the coupler 104 by means of wedge gripcoupling means such as shown in FIGURE 4, instead of the conventionalthreaded arrangement as just described.

It will be appreciated from the foregoing that the instant prestressingapparatus affords great versatility in providing tensioning forces forprestressing structural materials. Although the multiwire couplerillustrated in FIGURE 4 shows only four coextensive wire tendons, thesame basic structure has been employed to couple as many as 64 4 wirestogether, it being necessary to use a 2 /2" diameter bar on the otherside of the coupler, whereby the combined strength of the wires wassufficient to hold 650,000 pounds of tensile force. In addition, it is asimple operation with the instant apparatus to couple wire tendons inend to end relation, thus enabling construction of new concrete or otherprestressed structures in adjacent position to previously formedstructures. It is furthermore possible to make on the job assemblies ofthe instant wire tendons, rather than having to preassemble groups ofcoextensive wires at the factory prior to shipment to the constructionsite.

An important feature of the type of coupling as illustrated in FIGURES 4and 13 is that each end of the coupler may be designed and machined toattach the type or types of tendon or tendons to be connected theretowithout regard for the type or types of tendons to be connected to theopposite end of the coupler. This greatly assists in the economicmanufacture of the coupling, and the best utilization of material toattain a conpler of requisite strength in a minimum overall size.

I claim:

1. In a method for prestressing structural materials, the stepscomprising, providing a pair of generally elongated tendons each havinga protuberance adjacent one end thereof and an externally threadedsleeve concentrically mounted on said end for engagement with saidprotuberance, disposing said tendons in end to end relationship withsaid protuberances confronting one another, and threadedly engaging atubular internally threaded member with said two sleeve members tocouple said tendons together, and applying a tensioning force to saidtendons tending to pull them apart from one another.

2. In a method for prestressing a structural material, the stepscomprising, disposing a bearing plate in position for abuttingengagement with a structural material to be prestressed, securing anelongated tendon to said bearing plate which tendon has a protuberanceprovided adjacent one end thereof and an externally threaded sleeveconcentrically mounted thereon for engagement with said protuberance,disposing a second tendon in end to end relation with said first tendonwhich second tendon has a protuberance provided adjacent the end of saidtendon confronting said first tendon and an externally threaded sleeveconcentrically mounted thereon for engagement with said protuberance,and coupling said two tendons together by an internally threaded tubularcoupler threadedly engaging said two externally threaded sleeve members,and applying a tensioning force to said tendons tending to pull themapart from one another.

3. In. a method for prestressing structural materials, the stepscomprising, providing a first generally elongated tendon having aprotuberance adjacent one end thereof and an externally threaded sleeveconcentrically mounted on said end for engagement with saidprotuberance, providing a coupling member having threaded bores openingto opposite ends thereof, threadably engaging said sleeve in one of saidbores, threadably securing a second elongated tendon in another of saidbores in general end to end relationship With said first tendon, andapplying a tensioning force to said tendons tending to pull them apartfrom one another.

4. The method as defined in claim 3 providing a plurality of firstgenerally elongated tendons, each having a protuberance adjacent one endthereof and an externally threaded sleeve concentrically mounted thereonfor engagement of said protuberance, providing said coupling member witha plurality of threaded bores equal in number to said sleeves andopening to one of said ends and threadably securing said sleevestherein, disposing said.

5. The method as defined in claim 3, and forming said sleeve for saidfirst tendon of two separate generally half-tubular members eachexternally threaded and assembled to form an externally threaded sleeveconcentrically on said first tendon.

6. The method as defined in claim 3, forming said protuberance byconcentrically mounting on said first tendon an inner tubular memberhaving an externally tapered surface and formed for contracting intogripping engagement with said first tendon, and forming said sleeve withan internally tapered surface complementarily engaging said externallytapered surface, and radially contracting said inner tubular member whensaid sleeve is moved toward the proximate end of said tendon in responseto said tensioning force.

7. A method as defined in claim 6, and forming an abutment on saidproximate end of said tendon to set said inner tubular member.

References Cited UNITED STATES PATENTS 2,811,773 11/1957 Baskin 29-4523,029,490 4/1962 Middendorf 264-228 3,060,639 10/1962 Fields et al52-473 3,216,162 ll/1965 Gerber et al. 52-230 3,225,499 12/1965 Kourkene52230 3,255,558 6/1966 Middendorf 52223 JOHN F. CAMPBELL, Prima/yExaminer. T. H. EAGER, Assistant Examiner.

1. IN A METHOD FOR PRETRESSING STRUCTURAL MATERIALS, THE STEPSCOMPRISING, PROVIDING A PAIR OF GENERALLY ELONGATED TENDONS EACH HAVINGA PROTUBERANCE ADJACENT ONE END THEREOF AND AN EXTERNALLY THREADEDSLEEVE CONCONTRICALLY MOUNTED ON SAID END FOR ENGAGEMENT WITH SAIDPROTUBERANCE, DISPOSING SAID TENDONS IN END TO END RELATIONSHIP WITHSAID PROTUBERANCES CONFRONTING ONE ANOTHER, AND THREADEDLY ENGAGING ATUBULAR INTERNALLY THREADED MEMBER WITH SAID TWO SLEEVE MEMBERS TOCOUPLE SAID TENDONS TOGETHER, AND APPLYING A TENSIONING FORCE TO SAIDTENDONS TENDING TO PULL THEM APART FROM ONE ANOTHER.